Project Summary: Neuronal nicotinic acetylcholine receptors (nAChRs) are pentameric ligand-gated ion channels that mediate fast synaptic transmission and are important and novel therapeutic targets in neurodegenerative diseases and mental illness. Currently there is no atomic-resolution structure for any nicotinic receptor, and no receptor in this Cys-loop receptor superfamily has been structurally characterized in more than one conformation. The long-term objectives of the research are to better understand the conformational changes that underlie the transitions between different functional states and to develop reliable, atomic-resolution models of nAChRs relevant to structure-guided drug design. Toward these goals the following approach will be used. 1. Through receptor ortholog screening, identify an 7 receptor candidate for crystallization, and test conditions to optimize receptor stability in detergent. 2. Using fast-perfusion patch clamp and single channel analysis, test combinations of construct modifications and pharmacological probes to stabilize distinct receptor conformations. 3. Crystallize receptor in different conformational states and determine atomic-resolution structures of (a) a closed-resting receptor, (b) an open-activated receptor and (c) a closed-desensitized receptor. The structural studies will be complemented with functional assays that test new structure-based hypotheses regarding mechanisms of state transitions in the receptor. The results will have broad implications for the Cys-loop receptor family in general and 7 nAChRs specifically.